Composting is an excellent method of letting the nature take care of the degradation of organic waste, such as parts of plants, domestic waste and the like. Under different climatic conditions there are put different demands onto the structural design and shape of the composting plants, but it is a common positive thing for different plants, different temperatures and moisture contents, and for different material that is to be decomposed, if the material continuously is supplied with oxygen necessary for the degradation.
For this purpose it earlier has been suggested to design the composting device, as a drum rotatably arranged about a horizontal or slightly inclined axis and having a net covered outer side, which at the slow rotation (if the drum on one hand turns the material in the drum mechanically and on the other hand allows the oxygen of the air to reach the material to a big extent. Such a device is known e.g. from U.S. Pat. No. 3,966,415, but the disadvantage with this device is that the outside wall of the drum, which is provided with net meshes of uniform size, will spread the degraded material over a distance equal to the drum length, at the same time as different fractions of the degraded material will be mixed with each other. Furthermore with this device there is the risk that more coarse material, that lies closer to the drum wall, may prevent discharge of more degraded material situated closer to the centre of the drum.
From U.S. Pat. No. 3,245,759 is known a plant for fermentation of organic material, which works with forced air through-flow, and which consists of an elongated cylindric drum, rotatable about an axis being slightly inclined to the horizontal. At the infeed end of the drum is provided a sieve, against which material to be treated is advanced by a screw. After the sieve the interior of the drum is divided by a number of partition walls into a number of closed fermentation chambers, situated one after the other, and which partition walls each having one opening, which during a short part of a revolution of the drum transfers material from one chamber to the chamber situated nearest thereafter.
CA-B-613,004 describes a composting plant with a horizontally arranged rotatable drum, the interior of which is divided by sieve walls, each of which has a large central opening and a number of smaller meshes. All sieve walls are identical, i.e. they have the same mesh size, and this implies that no uniform size of particles is obtained at the discharge side of the plant, which is also further accentuated by the fact that larger non-mouldered pieces can pass to the next section through the large central openings of the sieve walls.
The purpose and most important features of the invention
The purpose of the invention is to provide a composting device, by means of which the entire compost mass is supplied with oxygen in a simple and efficient way without forced air supply, at the same time as all degradable material will be disintegrated into an essentially uniform fraction, which can be collected in a simple way, and which device furthermore must be reliable and comparatively cheap to obtain and to operate, and this has been achieved by means of the characteristics defined in the accompanying claims.